Cancer
What is Cancer? What causes Cancer?
Cancer also known as a malignant
tumor or malignant neoplasm is a group of diseases involving abnormal cell
growth with the latent to attack or spread to other parts of the body. Not all
tumors are cancerous; benign tumors do not spread to other parts of the body.
Possible signs and symptoms include: a new lump, abnormal bleeding, a prolonged
cough, unexplained weight loss, and a change in bowel movements, among others.
While these symptoms may indicate cancer, they may also occur due to other
issues. There are over 100 different known cancers that affect humans.
Cancer is a class of diseases
characterized by out-of-control cell growth. There are over 100 different types
of cancer, and each is classified by the type of cell that is initially
affected.
Cancer harms the body when
damaged cells divide uncontrollably to form lumps or masses of tissue called
tumors (except in the case of leukemia where cancer prohibits normal blood
function by abnormal cell division in the blood stream). Tumors can grow and
interfere with the digestive, nervous, and circulatory systems and they can
release hormones that alter body function. Tumors that stay in one spot and
demonstrate limited growth are generally considered to be benign.
More dangerous, or malignant, tumors form when two things occur:
1. A cancerous cell manages to move
throughout the body using the blood or lymph systems, destroying healthy tissue
in a process called invasion.
2. That cell manages to divide and
grow, making new blood vessels to feed itself in a process called angiogenesis.
How Cancer Spreads?
Scientists
reported in Nature Communications (October 2012 issue) that they have
discovered an important clue as to why cancer cells spread. It has something to
do with their adhesion (stickiness) properties. Certain molecular interactions
between cells and the scaffolding that holds them in place (extra cellular
matrix) cause them to become unstuck at the original tumor site; they become
dislodged, move on and then reattach themselves at a new site.
The researchers say this
discovery is important because cancer mortality is mainly due to metastatic
tumors, those that grow from cells that have traveled from their original site
to another part of the body. Only 10% of cancer deaths are caused by the
primary tumors.
Causes of Cancer
Tobacco use is the cause of about
22% of cancer deaths. Another 10% is due to obesity, a poor diet, lack of
physical activity, and consumption of ethanol (alcohol). Other factors include
certain infections, exposure to ionizing radiation, and environmental
pollutants. In the developing world nearly 20% of cancers are due to infections
such as hepatitis B, hepatitis C, and human papillomavirus. These factors act,
at least partly, by changing the genes of a cell. Typically many such genetic
changes are required before cancer develops. Approximately 5–10% of cancers are
due to genetic defects inherited from a person's parents. Cancer can be
detected by certain signs and symptoms or screening tests. It is then typically
further investigated by medical imaging and confirmed by biopsy.
Cancer is ultimately the result
of cells that uncontrollably grow and do not die. Normal cells in the body
follow an orderly path of growth, division, and death. Programmed cell death is
called apoptosis, and when this process breaks down, cancer begins to form.
Unlike regular cells, cancer cells do not experience programmatic death and
instead continue to grow and divide. This leads to a mass of abnormal cells
that grows out of control.
Cells can experience uncontrolled
growth if there are damages or mutations to DNA, and therefore, damage to the
genes involved in cell division. Four key types of gene are responsible for the
cell division process: Oncogenes tell cells when to divide, tumor suppressor
genes tell cells when not to divide, suicide genes control apoptosis and tell
the cell to kill itself if something goes wrong, and DNA-repair genes instruct
a cell to repair damaged DNA.
Cancer occurs when a cell's gene
mutations make the cell unable to correct DNA damage and unable to commit
suicide. Similarly, cancer is a result of mutations that inhibit oncogene and
tumor suppressor gene function, leading to uncontrollable cell growth.
Carcinogens
Carcinogens are a class of
substances that are directly responsible for damaging DNA, promoting or aiding
cancer. Tobacco, asbestos, arsenic, radiation such as gamma and x-rays, the
sun, and compounds in car exhaust fumes are all examples of carcinogens. When
our bodies are exposed to carcinogens, free radicals are formed that try to
steal electrons from other molecules in the body. Theses free radicals damage
cells and affect their ability to function normally.
Other Medical Factors Holding Hands
As we age, there is an increase
in the number of possible cancer-causing mutations in our DNA. This makes age
an important risk factor for cancer. Several viruses have also been linked to
cancer such as: human papillomavirus (a cause of cervical cancer), hepatitis B
and C (causes of liver cancer), and Epstein-Barr virus (a cause of some
childhood cancers). Human immunodeficiency virus (HIV) - and anything else that
suppresses or weakens the immune system - inhibits the body's ability to fight
infections and increases the chance of developing cancer.
What is Cancer?- Video
How Cancer can be Prevented?
Many cancers can be prevented by
not smoking, maintaining a healthy weight, not drinking too much alcohol,
eating plenty of vegetables, fruits and whole grains, being vaccinated against
certain infectious diseases, not eating too much red meat, and avoiding too
mucch exposure to sunlight. Early detection through screening is useful for
cervical and colorectal cancer. The benefits of screening in breast cancer are
controversial. Cancer is often treated with some combination of radiation
therapy, surgery, chemotherapy, and targeted therapy. Pain and symptom
management are an important part of care. Palliative care is particularly
important in those with advanced disease. The chance of survival depends on the
type of cancer and extent of disease at the start of treatment. In children
under 15 at diagnosis the five year survival rate in the developed world is on
average 80%. For cancer in the United States the average five year survival
rate is 66%.
Cases of Cancer
In 2012 about 14.1 million new
cases of cancer occurred globally (not including skin cancer other than
melanoma). It caused about 8.2 million deaths or 14.6% of all human deaths. The
most common types of cancer in males are lung cancer, prostate cancer,
colorectal cancer, and stomach cancer, and in females, the most common types
are breast cancer, colorectal cancer, lung cancer, and cervical cancer. If skin
cancer other than melanoma were included in total new cancers each year it
would account for around 40% of cases. In children, acute lymphoblastic
leukaemia and brain tumors are most common except in Africa where non-Hodgkin
lymphoma occurs more often. In 2012, about 165,000 children under 15 years of
age were diagnosed with cancer. The risk of cancer increases significantly with
age and many cancers occur more commonly in developed countries. Rates are
increasing as more people live to an old age and as lifestyle changes occur in
the developing world. The financial costs of cancer have been estimated at
$1.16 trillion US dollars per year as of 2010. In 2007, cancer claimed the lives
of about 7.6 million people in the world. Physicians and researchers who
specialize in the study, diagnosis, treatment, and prevention of cancer are
called oncologists.
What are the Symptoms of Cancer?
Cancer symptoms are quite wide-ranging
and depend on where the cancer is located, where it has spread, and how big the
tumor is. Some cancers can be felt or seen through the skin - a lump on the
breast or testicle can be an indicator of cancer in those locations. Skin
cancer (melanoma) is often noted by a change in a wart or mole on the skin.
Some oral cancers present white patches inside the mouth or white spots on the
tongue.
Other cancers have symptoms that
are less physically apparent. Some brain tumors tend to present symptoms early
in the disease as they affect important cognitive functions. Pancreas cancers
are usually too small to cause symptoms until they cause pain by pushing against
nearby nerves or interfere with liver function to cause a yellowing of the skin
and eyes called jaundice. Symptoms also can be created as a tumor grows and
pushes against organs and blood vessels. For example, colon cancers lead to
symptoms such as constipation, diarrhea, and changes in stool size. Bladder or
prostate cancers cause changes in bladder function such as more frequent or
infrequent urination.
As cancer cells use the body's
energy and interfere with normal hormone function, it is possible to present
symptoms such as fever, fatigue, excessive sweating, anemia, and unexplained
weight loss. However, these symptoms are common in several other maladies as
well. For example, coughing and hoarseness can point to lung or throat cancer
as well as several other conditions.
When cancer spreads, or
metastasizes, additional symptoms can present themselves in the newly affected
area. Swollen or enlarged lymph nodes are common and likely to be present
early. If cancer spreads to the brain, patients may experience vertigo,
headaches, or seizures. Spreading to the lungs may cause coughing and shortness
of breath. In addition, the liver may become enlarged and cause jaundice and
bones can become painful, brittle, and break easily. Symptoms of metastasis ultimately
depend on the location to which the cancer has spread.
How is cancer classified?
There are five broad groups that
are used to classify cancer.
Carcinomas are characterized by
cells that cover internal and external parts of the body such as lung, breast,
and colon cancer.
Sarcomas are characterized by
cells that are located in bone, cartilage, fat, connective tissue, muscle, and
other supportive tissues.
Lymphomas are cancers that begin
in the lymph nodes and immune system tissues.
Leukemias are cancers that begin
in the bone marrow and often accumulate in the bloodstream.
Adenomas are cancers that arise
in the thyroid, the pituitary gland, the adrenal gland, and other glandular
tissues.
Cancers are often referred to by
terms that contain a prefix related to the cell type in which the cancer
originated and a suffix such as -sarcoma, -carcinoma, or just -oma. Common
prefixes include:
Adeno- = gland
Chondro- = cartilage
Erythro- = red blood cell
Hemangio- = blood vessels
Hepato- = liver
Lipo- = fat
Lympho- = white blood cell
Melano- = pigment cell
Myelo- = bone marrow
Myo- = muscle
Osteo- = bone
Uro- = bladder
Retino- = eye
Neuro- = brain
How is cancer diagnosed and staged?
Early detection of cancer can
greatly improve the odds of successful treatment and survival. Physicians use
information from symptoms and several other procedures to diagnose cancer.
Imaging techniques such as X-rays, CT scans, MRI scans, PET scans, and ultrasound
scans are used regularly in order to detect where a tumor is located and what
organs may be affected by it. Doctors may also conduct an endoscopy, which is a
procedure that uses a thin tube with a camera and light at one end, to look for
abnormalities inside the body.
Cancer Testing
Extracting cancer cells and
looking at them under a microscope is the only absolute way to diagnose cancer.
This procedure is called a biopsy. Other types of molecular diagnostic tests
are frequently employed as well. Physicians will analyze your body's sugars,
fats, proteins, and DNA at the molecular level. For example, cancerous prostate
cells release a higher level of a chemical called PSA (prostate-specific
antigen) into the bloodstream that can be detected by a blood test. Molecular
diagnostics, biopsies, and imaging techniques are all used together to diagnose
cancer.
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